Update: No sooner do we post about the issue, and it's back up. However, that just makes this a cautionary tale--Xbox Live continues to have issues, and so if you can't sign into the service, then go check out the status page and see what's up.
Xbox Live has been having issues recently. Yesterday it was problems with signing into the service and with running the new Backward Compatibility title Galaga. Today, it's more issues with signing in, and it's affecting users on the Xbox One, Xbox 360, and Windows 10.
As always, you can head on over to the Xbox Live status page, click on the "Notify me" button, enter your phone number, and get notified via text or robocall when the system is back online. We'll keep our eyes open as well, and here's to hoping that Microsoft gets these intermittent issues rectified soon.